The present invention relates to gas sampling devices, and more particularly to probes for use in sampling particulates in air.
In sampling engine exhaust, such as aircraft turbine engine exhaust, for the purpose of determining the particulate concentration in the exhaust, exhaust samples have been drawn through a hollow probe, whose upper portion has been bent at a right angle, to a particulate collector. A flexible line connects the probe to the particulate collector. Under test, a continuous sample of the exhaust is taken for a fixed period of time, such as an hour. During this time, an unknown amount of particulate material adheres to the inner walls of the probe and the flexible line. After the test, when the engine is shut down, the probe and line are removed from the engine along with the particulate collector. The particulate material should be removed as completely as possible from the inside of the probe and line, in order to obtain uniform results in successive measurements and prevent interference by particulates left over from previous tests with intake and passage of particulates in a subsequent test. Also, particulates in the exhaust sample which are deposited in the sampling probe will not be accounted for by the particulate collector, although these particulates were in the exhaust sample taken. Removal of the particulate material residue in the sample line can be accomplished by pouring small amounts of a solvent such as chloroform into one end of the probe and line and swirling it back and forth therein. The solvent is then poured into a clean glass or plastic bottle. This procedure is repeated until the solvent appears clean after the probe and line, usually requiring several washings. In the laboratory the probe and line washings are poured into a preweighed clean glass beaker. Additional chloroform is used to wash out the inside of the sample bottle. The solvent is then allowed to evaporate, after which the beaker and residue are weighed. The difference between tare and gross weight of the beaker indicates the amount of material accumulation in the probe and sample line. This process requires that the probe and line be completely removed from the engine and taken to an area where they can be washed out. Furthermore, a quantity of chloroform or other solvent must be available at the test site to wash out the probe and line. Chloroform in particular should be used only if there is adequate ventilation to avoid prolonged inhalation of its vapor. It is also highly flammable. Also, during the probe and line washing procedure, spillage of the solvent/particulate solution is a possibility, as is the uncertainty of removing all particulate material from inside the probe and line. Either possibility could compromise the validity of the final weight of the collected particulate material. In addition, 2 to 3 days are required for the solvent to completely evaporate, after which the beaker must be weighed again. Thus, the entire procedure requires a substantial amount of time.